Computational Investigation on Hydrodeoxygenation (HDO) of Acetone to Propylene on α-MoO₃ (010) Surface

Abstract

Density functional theory (DFT) calculations were performed on the multistep hydrodeoxygenation (HDO) of acetone (CH 3 COCH 3 ) to propylene (CH 3 CHCH 2 ) on a molybdenum oxide (α-MoO 3 ) catalyst following an oxygen vacancy-driven pathway. First, a perfect O-terminated α-MoO 3 (010) surface based on a 4x2x4 supercell is reduced by molecular hydrogen (H 2 ) to generate a terminal oxygen (O t ) defect site. This process occurs via a dissociative chemisorption of H 2 on adjacent surface oxygen atoms, followed by an H transfer to form a water molecule (H 2 O). Next, adsorption of CH 3 COCH 3 on the oxygen deficient Mo site forms an O-Mo bond, then the chemisorbed CH 3 COCH 3 forms CH 3 COCH 2 by transfer of an H atom to an adjacent O t site. The surface bound hydroxyl (OH) then transfers the H atom to the immobilized O atom, to form surface bound enol, CH 3 CHOCH 2 . The next step releases CH 3 CHCH 2 into the gas phase, whilst simultaneously oxidizes the surface back to a perfect O-terminated α-MoO 3 (010) surface. The adsorption of H 2 , and the formation of a terminal oxygen (O t ) vacancy moves the conduction band minimum (CBM) from 1.2 eV to 0 and 0.3 eV, respectively. Climbing image nudged elastic band (CI-NEB) calculations using a Perdew-Burke-Ernzerhof (PBE) functional in combination with double-zeta valence (DZV) basis sets indicate that the dissociative adsorption of H 2 is the rate-limiting step for the catalytic cycle with a barrier of 1.70 eV. Furthermore, the lower barrier for surface mediated H transfer from primary to secondary carbon atom (0.63 eV) compared to that of a concerted direct H transfer to the secondary C atom with simultaneous desorption (2.02 eV) emphasizes the key role played by the surface in H transfer for effective deoxygenation.

A Coupled Density Functional Theory–Microkinetic Modeling for the Hydrodeoxygenation of Glycerol to Propylene on MoO3

“…Moreover, two studies were performed on α-MoO 3 (010) using periodic slabs: the HDO of acetaldehyde 45 and acetone. 46 The vacancy formation and the HDO mechanism were reported in both studies. They were performed with pure density functional theory (DFT), which tends to the overdelocalization of d and f electrons of reducible transition metal oxides (RTMOs) due to the selfinteraction error (SIE).…”

Learning from the past: Are catalyst design principles transferrable between hydrodesulfurization and deoxygenation?

“…However, the authors also reported moderate deactivation of the carbide and oxide catalysts under HDO condition and phosphide had the highest selectivity to the undesired hydrogenation product methyl‐cyclopentane. Román‐Leshkov and coworkers successfully demonstrated the remarkable activity and selectivity for HDO of model bio‐oil oxygenates on MoO 3 and supported MoO 3 , and proposed a (reverse) Mars van Krevelen type reaction mechanism . The importance of oxygen vacancy formation for HDO of acetaldehyde on MoO 3 (010) was also discussed in the periodic DFT study by Mei et al, as well as in Moberg et al's investigation of the HDO of acrolein using cluster models of MoO 3 in Gaussian 03 .…”

Adsorption of Biomass-Derived Products on MoO3: Hydrogen Bonding Interactions under the Spotlight

“…28,29 On the other hand, using molecules with high molecular weight together with periodic crystal models with an accurate method is always an issue for getting useful information; then small molecules and cluster models have been used computationally. 30,31 The presence of the oxygen atoms with phenolic or acidic functionalities in the biomass-related products contributes with hydrogen-bonding interactions. Understanding the H-bonds in catalytic processes is very important for a better interpretation of the adsorption phenomena as well as stabilization of substrates or intermediates.…”